Hearing impairment, to a greater or lesser extent, affects more than 30 million people in the United States, according to the American Academy of Audiology. Hearing impairment can affect its victim in a variety of ways, such as a reduced comprehension of conversation or spoken words, or reduced ability to hear and enjoy music.
Many technologies have been developed to reduce the impact of hearing impairment on those who suffer from it. These technologies include a variety of hearing aids, diagnostic techniques and related devices. Moreover, the improvement of the clarity and intelligibility of audio signals by means of electrical devices has been the object of much investigation, especially for applications in telephony, recording and playback of audio signals for the hearing impaired. The results of previous research in these areas is described in various patent applications, including the following commonly-owned applications: Provisional Patent Application 60/837,752 filed Aug. 15, 2006, patent application Ser. No. 11/188,519 filed Jul. 25, 2005, and patent application Ser. No. 10/864,691 filed Jun. 9, 2004. Application Ser. Nos. 11/188,519, and 10/864,691 are incorporated herein by reference.
The mechanisms of sound propagation and enhancement are complex phenomena which have been the subject of considerable study. While counter-intuitive in concept, researchers have discovered that under certain conditions, human hearing may be enhanced by the addition of noise, which may actually improve signal detection, an effect attributable to a phenomena known as stochastic resonance. Stochastic resonance occurs when random noise is added to a signal, often at very low levels, which enhances the signal to noise ratio in such a way as to drive normally inaudible or barely audible sounds, such as the quiet or softer sounds of a musical passage, above the detection threshold. Hence, at a given output volume setting on a system, such as a radio, the overall quality of the sound is improved, as opposed to the sound which would be heard by a listener who simply turned up the volume to hear a faint signal. In the latter situation, the listener would turn up the noise level as well, to the detriment of the overall quality of the system output.
With respect to hearing impaired individuals, hearing loss may occur over the entire range of audible frequencies or, alternately, over only a portion of or at a single frequency within the audible range. Accordingly, it would be desirable to have the capability of selecting a single frequency or a range of frequencies at which the resonance phenomenon described above occurs, preferably in a system which could be tuned by the user to compensate for his or her specific audio impairment.